THE CONNECTIVE SUBSTANCE GKOUP. 



91 



The arrangement just described is found in all compact 

 bone where there is any considerable thickness, but when, as 

 in flat bones, the cortex is very thin, the lamellae often pursue 

 a straight arid parallel course. Some of these lamellae or plates 

 exhibit transverse striations ; others are homogeneous. 



In Fig. 35 may be seen the lacunae lying between the 

 lamellae. They appear 

 as dark spaces disposed 

 at quite regular intervals 

 and, having their long 

 axes parallel with the 

 course of the lamellae. 

 Laterally each corpuscle 

 gives off numbers of pro- 

 cesses, many of which 

 branch, while all, or near- 

 ly all, anastomose with 

 corresponding branch- 

 lets of other corpuscles- 

 A branchlet is also given 

 off from the end of each 

 corpuscle, and forms a 

 connection with the adjacent bodies lying in the same inter- 

 lamellar space and in the same plane. 



The Haversian canals form a broad-meshed network through- 

 out the bone, establishing a communication between the central 

 marrow cavity and the external surface of the bone (Fig. 36). 



The arrangement of parts comprised by each Haversian 

 canal, with its investing lamellae, and interposed lacunae and 

 their anastomosing carialiculi constitutes an Haver sian system. 

 Though found mainly in the compact tissue, they may also be 

 seen in the large trabeculae of the spongy substance. As seen 

 in Fig. 36, the Haversian canals form a network of which the 

 longitudinal tubes are the larger and longer. Besides convey- 

 ing blood-vessels and lymphatics they have a certain amount 

 of connective tissue which varies according to the locality, and 

 establishes a more or less complete connection between the con- 

 nective tissue of the marrow cavity and of the periosteum. 



In young bone this is well seen ; in adult bone the direct 

 continuity can with difficulty be traced, as the vessels are apt 

 to till the tubes pretty completely. 



PIG. 35. Transverse section of human femur, deprived of 

 inorganic material by hydrochloric acid. (Rollett.) 



